The present invention relates to an electronic control apparatus, cooperating, for instance, with a stepwise operating machine, device, or the like, which performs sequences of step on a programmed basis.
The control apparatus, in accordance with the invention, is particularly destined and designed to cooperate with a selection switch for program selection, and each of the selectable and selected programs is contained in a PROM, preferably being of the electrically programmable and erasable variety, also called EPROM, sometimes called EAROM. Program control on the basis of PROM's or E-PROM's is used to an increasing extent in many fields of application. Utilization of PROM's (rather than ROM's) is advisable in those cases in which one or the other, some, or even all, programs may have to be changed, extended, augmented, modified, replaced, etc.
In practice, it was found necessary to take the PROM physically out of the circuit in order to achieve the reprogramming, or the like. The basic reason here is to be seen in the fact that rewriting the content of a PROM requires higher than normal operating voltages. This reprogramming voltage, if effective in regular circuit elements, would readily destroy them.
Usually, a PROM is one of several IC elements on a PC board. The removability requires that a socket be affixed to that board, and the IC-PROM is simply plugged in or taken out. This appears to be a simple enough procedure; but in practice, it was found that untrained personnel may damage this part or others, or plug the PROM back in the wrong orientation. Thus, the approach to the problem of reprogramming, namely, the removable mounting of the PROM on the PC board, and providing for external reprogramming of the removed PROM, is not a satisfactory one.